The Lord of the Rings, The Battle for Middle-earth II

I find the best strategy for goblins is to continually harass the enemy's resources with the faster units like spiderlings and spider riders. If they have walls or random buildings left unguarded use the giants who have exceptionally long range to take them out. Unlike other factions where you can win with only one or two different units(like the elves and the mirkwood archers) you need to balance your army with several different units. so if against elves make more spider riders and maurader trolls.

When you're Goblins harassment is key. Half-orcs are really strong, and fairly cheap.
When you're mordor go for haradrim and later get a couple of attack trolls.

I usually keep my fighter-archer ratio at 3:2

For Isengard, buy Lurtz immediatly to hold off enemy troops while you build up recource buildings and an army. Then, you rush, building a simple wall around your Fortress while you do it.